This invention relates to a novel process for the production of corrugated paperboard adhesive and to the novel adhesives thus produced.
Corrugated paperboard adhesives having a cooked or carrier portion and an uncooked or secondary portion are conventionally produced from pearl corn starch, or, to a lesser extent, from tapioca or wheat starch. However, in U.S. Pat. Nos. 3,775,144 and 3,775,145, Alan M, Hill and I disclose processes employing high pressure steam in a jet cooker, which permits the use of flour instead of starch in the carrier portion. In U.S. Pat. No. 3,859,108, we disclose such a process for the production of a size for paper, in which optionally the flour is first subjected to a viscosity reducing treatment with enzyme or hydrogen peroxide.
It has been known for over 10 years that a corrugated adhesive whose carrier portion is prepared from a high amylose (about 80%) starch is superior to one prepared from pearl starch, which contains about 27% amylose because a higher solids content carrier can be produced having rheological properties comparable to carriers of lower solids content produced from pearl starch. High amylose starch was originally produced by alcohol precipitation and was exxtremely expensive, viz., about $100/cwt. compared to about $9/cwt. currently for pearl starch. After corn hybrids were developed from which a starch having an 80:20 ratio of amylose to amylopectin could be produced, its use as a corrugated adhesive became feasible. Such a starch is sold by National Starch under the trademark "Vinamyl." That starch is still expensive, its current price being about 3-4 times that of pearl starch.
Although the advantages of a high amylose starch over conventional pearl starch as a corrugated starch has been known for at least 10 years and although it is known that starch pastes can be thinned with hydrogen peroxide, to date no method has been developed which can cheaply convert conventional low amylose starches using standard equipment present in all corrugating plants, into a corrugated adhesive having the properties of an adhesive produced from a high amylose starch, such as "Vinamyl."
It is an object of this invention to provide such a process. It is another object to provide novel Stein-Hall type composite corrugated paperboard adhesives produced according to the process of this invention. Other objects will be apparent to those skilled in the art to which this invention pertains.